The present invention relates to a method and apparatus for applying a tensioned elastic member transversely to a moving web of material. More specifically, the apparatus is useful for applying waist zone elastic to a moving assembly in the manufacture of disposable diapers.
Longitudinally positioned elastic in the leg encircling zones of disposable diapers represented a major improvement in the reduction of leakage. A diaper of this type is shown generally in U.S. Pat. No. 3,860,003 to Buell. Machinery for manufacturing the above diaper is described in U.S. Pat. No. 4,081,301 to the same inventor. Subsequent to this time, other inventors in the field have placed elastic in the waist area in order to ensure a more comfortable and leak resistant fit. Examples of diapers of this type are seen in U.S. Patents to Schaar, U.S. Pat. No. 3,951,150; Repke et al, U.S. Pat. No. 4,205,679; Sciaraffa et al, U.S. Pat. No. 4,381,781 and Repke et al, U.S. Pat. No. 4,430,086. The references just cited are intended to be exemplary and not inclusive.
Diapers are normally manufactured in a continuous end-to-end assembly. While the exact manufacturing process will vary somewhat between different manufacturers, most typically preformed absorbent pads of fluffed wood pulp are laid down in a spaced-apart relationship on a continuous sheet of thin polyethylene. These are then covered with a nonwoven fabric which forms the skin contacting surface when in use. Many variations occur in this general procedure including the application of leg elastic, and adhesive attachment tabs in what will become the waist area. One could assume that the application of longitudinally oriented elastic to the moving diaper assembly would be a relatively simple operation. That this is not so is well shown by the considerable number of United States and foreign patents directed to the problem. However, the application of transversely oriented elastic to the waist areas of a continuous assembly moving at high speed represents engineering difficulties of a much greater magnitude. This problem has not yet been solved to the satisfaction of most diaper manufacturers. Reference can be made to Joa, U.S. Pat. No. 4,284,454; Rega, U.S. Pat. No. 4,240,866; Spencer, U.S. Pat. No. 4,523,969; and Van Vliet, U.S. Pat. No. 4,726,874 as examples of machinery for applying transverse elastic. The Spencer patent describes apparatus having a plurality of heads moving orbitally along an elliptical path. These heads are designed to receive and hold two parallel strips of tensioned elastic. As the head is moving at its greatest velocity, at the end of its eliptical path, it contacts the transversely moving diaper assembly and transfers the elastic to the polyolefin backing film. A rotating mechanism attached to each head ensures that they remain oriented with their longitudinal axes always parallel as they travel around a central drive unit. The path of travel is controlled by a cam and follower mechanism which increases the radius of travel in the application zone.
The Van Vliet apparatus has a supporting frame with a shaft providing an axis of rotation for at least one rotatable radial arm. A polygonal head is mounted at the end of each arm. This has a number of peripheral edges with clamps or vacuum orifices for holding a tensioned strand or strands of elastic ribbon. A drive rotates the radial arm and a rotating mechanism moves the heads (360/n).degree. for each full rotation of the radial arm, where n is equal to the number of peripheral faces on the head. An anvil acts against the head at the time of application of the tensioned elastic to the moving web. The web is passed between the head and the anvil along a path describing a chord or tangent of the circle of rotation of the radial arms.
Young et al, in U.S. Pat. No. 4,726,807 describe another system for making a diaper with an elasticized waistband. This uses as an insert portion of a material which is relatively inelastic as supplied but which becomes elastic upon heating. Alternatively, the entire moisture impermeable backing sheet may be made of the material.
The above-noted examples of machinery for applying transversely oriented elastic to a diaper assembly have been not entirely satisfactory for a number of reasons. In an effort to develop a superior system, the present inventor has searched other fields where a transversely moving first component is applied to a second component moving at right angles. In the field of bag making, U.S. Pat. Nos. 4,289,567 and 4,279,686 to Achelpohl might be noted. However, in this case the machinery operates in intermittent fashion with the second element being stopped during the period when the transversely moving first element is applied. This situation is similar to that shown by Wilson in U.S. Pat. No. 4,316,756 and 4,357,197 where pocket blanks are being applied in intermittent fashion to a moving garment portion. Urban et al, in U.S. Pat. No. 4,135,343 shows a similar intermittent operation where film is being enclosed within a paper mount to form photographic slides. Intermittent operation is also found in U.S. Pat. No. 2,601,005 to Rainey in apparatus to mount lead wires to a capacitor laminate and in U.S. Pat. No. 3,960,641 to Pedersen where handle reinforcements are being placed on carrier bags. In the case of the latter inventor, opposed hexagonal rotary heads carry reinforcement labels which are applied to a moving strip of bag stock. At a second operation remote from this one, elongated hand holds are punched.
Truly continuous operation has been achieved in the diaper industry in the application of waistband adhesive attachment tapes. Examples of equipment to accomplish this function are shown in Wierzba et al, U.S. Pat. No. 3,728,191 and Babcock, U.S. Pat. No. 3,897,293. Endres, in U.S. Pat. No. 3,520,303, shows application of a barrier strip overlying the ends of an absorbent diaper pad. This represents a different and much simpler problem than that of applying a tensioned elastic article. In the latter case the elastic must generally be held in tension while it is bonded to the backing sheet or one of the other diaper components. This requirement greatly complicates the design of suitable machinery.